Brand new member love the people and the info posted here first off motor has been replaced with a 03 Pontiac 3.8 supercharged original motor chev 3.8 sfi fuel system builds pressure in fuel tank scan tool indicates po449 should vent valve be under vacuum or push air into tank not sure I think it may be hooked up backwards also car is running on original ecm for 2000 3.8 but it doesn't shift right engine performance is erratic bad fuel economy seems like it run different each time it's started sometimes runs great excellent power other times idles rough misfires without having made any adjustments is it possible that supercharger is confusing ecm

 

Was the tune for the new engine loaded into the pcm?

The supercharged engine has different size fuel injectors, a 2 bar MAP instead of a 1 bar, as well as a different size MAF opening. The tune for the new engine has to be loaded into the pcm to run correctly.

 

pcm has not been loaded is zz performance a good option and I will check on map opening thanks 👍

 

It is not a map opening. The sensor itself is different. The 2 bar MAP is required to read boost.
The PCM not being reprogrammed for the L67 3800 SC is where a bulk of your problems are going to be. It is currently trying to feed this as if it is not a supercharged engine and like Bumpin' mentioned it also has different size injectors, the MAF is not going to read right due to differences in the opening. Before chasing down a bunch of performance issues, you will need to get the PCM addressed. ZZP should be able to assist.

 

You need to park the car until its updated then. It shouldn't be driven and I wouldn't even bother starting it personally. Its never going to run right until it at least gets a stock L67 engine map loaded.

I will say it likely won't fix the gas tank issue - thats probably something else going on, but the engine issues are most certainly related.

 

I have the 03 Pontiac ecm that was in the car motor came out of but I can't get past security what's crazy is chev ecm pcm bcm Pontiac key switch did re learn and it runs but was never able to get it started with Pontiac ecm would always run for 3 seconds then die

 

Probably something weird with security on the 03. Honestly any swap I've been involved with I've always used 98-02 GP stuff. 97s and 03s both had some oddities, and of course 04+ have several changes.

If you knew someone with a tuner locally, there are some security settings to play with on the 03 to try to make it happy but honestly its probably not worth the hassle to keep screwing with it as it sounds like you've already got a good bit of time into trying to get it to work.

The best bet would be to find a local member with DHP PT or HPT. They could pull stock tables for a L67 and flash them to your current computer in minutes. ZZP is a viable option, as are any place that specializes in 3800s and does canned tunes by mail. Theres just added time and a bit of added risk of something not getting flashed 100% right and having to send it back to be redone. Not the end of the world, but for pcm changes as simple as this, its easier if you can find a local.

 

So you are aware, these cars have three computers.
PCM - Performance Control Module. Controls all engine and transmission items. This has the VIN programmed into it and is part of the anti-theft system.
BCM - Body Control Module. This controls all car functions (door locks, all lights, windows and such). This has the VIN programmed into it and is part of the anti-theft system.
EBCM - Electronic Brake Control Module (aka the ABS computer). Controls ABS. Does NOT have the VIN programmed and is NOT part of the anti-theft system.

The Factory Radio does store the VIN (but just for the radio's anti-theft system). And the lock cylinder has a chip in it that makes the third part of the vehicle anti-theft system.
The fact you got past the anti-theft but then the car runs for 3 seconds, actually sounds like part of the anti-theft system (PCM was approved to start but then something caused a problem running and deactivated the car). I ran into that with some goofing I was doing last year with anti-theft. And it could just be a weird difference mixing/matching years of parts, maybe the wrong VIN in the PCM. Not sure.
Goes back to a vendor like ZZP is most likely the best option to fix the PCM for your needs.